During operation, internal combustion engines generate various combustion by-products that are emitted from the engine in an exhaust stream. As such, various approaches may be utilized in order to reduce regulated emissions. In some examples, nitrogen oxide (NOx) emissions may be reduced by employing exhaust gas recirculation (EGR), carrying out combustion in the engine with a Miller cycle, and/or including an exhaust gas treatment system with a device such as a NOx trap in an exhaust passage of the engine.
In other examples, the inventors herein have recognized the exhaust gas treatment system may include devices such as a diesel oxidation catalyst (DOC) and a particulate oxidation catalyst (POC) to reduce particulate matter emissions. However, when the exhaust gas treatment system including the DOC and POC is positioned downstream of a turbocharger, specific fuel consumption may be increased resulting in decreased fuel efficiency. On the other hand, when the exhaust gas treatment system including the DOC and POC is positioned upstream of a turbocharger, a transient response time of the engine may be increased during engine loading, as a portion of exhaust thermal energy is absorbed by the exhaust gas treatment system before the exhaust gas flow reaches the turbocharger.